1. Field of the Invention
This invention generally relates to coupling of radiant energy from a radiant energy source to the conducting medium of a primary optical system, and in particular to a termination arrangement or connector for coupling laser energy to an optical fiber system, and to a method of manufacturing or assembling such a termination or connector.
The invention allows for focusing a fixed spot into a smaller core fiber by utilizing refractive properties of a transparent ferrule surrounding the entrance surface of the fiber, while avoiding manufacturing and heat transfer problems associated with the fiber termination disclosed in U.S. Pat. No. 6,282,349 (Griffin).
The invention may be used in a variety of laser deliver systems including, by way of example and not limitation, medical laser applications such as the laser delivery apparatus with safety feedback disclosed in copending U.S. patent application Ser. Nos. 11/510,691 and 11/714,785, and the venous ligation methods and systems disclosed in U.S. Pat. No. 6,398,777 (Diomed) and U.S. Patent Application Publication No. 2004/0092913 (Hennings). Furthermore, by enabling coupling to smaller, more flexible fibers, the invention makes it possible in certain medical applications, to entirely eliminate the need for an introducer or catheter to guide the fiber to the treatment area.
2. Description of Related Art
In optical fiber applications where fiber size or flexibility is important, a problem often arises in that it is difficult to couple light to the fiber, either because the fiber has a core diameter smaller than the focused spot of the laser source, the focused spot is not precisely aligned with the fiber, and/or the acceptance angle is too small to accept all of the focused radiant energy. This reduces the efficiency of the delivery system, limiting the amount of energy that can be delivered, and in addition raises the possibility of damage to the fiber termination and/or connector, or of unwanted coupling of light to the cladding of the fiber, which can cause damage downstream from the termination. A discussion of the problems associated with stray light, and solutions involving various arrangements for dissipating or deflecting uncoupled light away from the fiber cladding and/or vulnerable components of the termination connector is found in copending U.S. Pat. No. 7,204,645, herein incorporated by reference.
In addition to the deflection/dissipation approach to radiation that fails to couple to the fiber core, U.S. Pat. No. 7,204,645 proposes tapering the input end of the fiber in order to increase the size of the surface through which radiation enters the fiber. However, the use of tapers has the disadvantage of enabling light to enter the fiber at increased angles of incidence, thereby creating higher order propagation modes which limit the bend performance of the fiber or alter the output.
Alternatively, it has been proposed to increase the coupling surface area by fusing a cylindrical glass ferrule to the end of the fiber, as disclosed for example in U.S. Pat. No. 6,282,349 (Griffin). As described therein, an optical fiber, which has at least a silica core and a polymer external jacket, is attached to a quartz ferrule by stripping the external jacket from a length of the end of the optical fiber to expose a portion of the silica core. The inner core of the fiber is inserted into the bore in the quartz ferrule, and is fused to the quartz ferrule by means of heat fusion, without employing any adhesives, to bond the ferrule and the optical fiber together. A metal beam block surrounds at least a portion of the quartz ferrule on the side where the optical fiber is inserted into it. The beam block includes an extension surrounding the polymer external jacket of the fiber, and the extension is crimped onto the polymer jacket to hold the beam block and fiber in place.
In the Griffin patent, heat fusion of the inner core of the fiber to the quartz ferrule is accomplished by means of laser energy, either end-on or from the side with rotation of the quartz ferrule and the included fiber core. In principle, the heat fusion should form an integral glass end on the ferrule which securely locks the fiber to the ferrule. However, it has been very difficult in practice to implement the heat fusion proposed by Griffin in practice. The reason is that the quartz ferrules are too thick (typically ˜2 mm in diameter) for a CO2 laser to penetrate and fuse the fiber to the quartz ferrule. In addition, by attaching a beam block to the quartz ferrule in order to prevent damage during fusion, Griffin fails to provide a way to adequately deflect or dissipate radiation that fails to couple to the core through the quartz ferrule, and therefore the Griffin arrangement still presents a risk of damage to the connector. Still further, like the tapered fiber termination, the quartz ferrule arrangement of Griffin is still subject to creation of higher order propagation modes.